This invention relates to continuous mining machines engaged in the process of extracting mineral, i.e. coal, trona, etc., from an underground seam. More particularly this invention relates to methods and apparatus employed to detect the location of seam boundaries and to guide the machine to achieve the desired cutting horizons (vertical elevations) relative to those seam boundaries.
Continuous mining machines typically include a self-powered, tracked vehicle having a rotary arm pivotally mounted at its forward end. A cutter is rotatably mounted at the distal end of the rotary arm to cut into a coal or ore seam for extraction of the coal or ore by an extraction mechanism provided on the machine.
Various patents exist which describe devices utilized in the mining of coal. Most notably the Lipinsky U.S. Pat. No. (4,952,000) which describes the method and apparatus of HIWALL mining. Lipinsky relies on gamma ray detection as a sensor. However, Lipinsky has determined that mining data on the use of the gamma detectors in Lipinky""s invention is limited in significant ways. Lipinsky uses gamma detectors ONLY to measure coal thickness that MUST be left at the roof and the floor of the mined highwall holes. Lipinsky further records coal thickness data on one or more holes, creating a profile of that seam, and then applies the resulting vertical control scheme to the machine on the next adjacent hole. He does not use real time data to try and control the machine in any current hole, but relies on the data on the previously recorded hole to assume what will happen ahead of the machine in the current hole. While he is controlling the machine in the current hole, he is recording data to then be applied to the next hole.
Lipinsky has determined that using data on any current hole for controlling the machine in that current hole is inadequate and not useful, due to the fact that no one has derived a good control scheme to predict what is ahead of the miner. The present control scheme has, however, successfully used real-time data to control the machine in the current tunnel, which would be required in normal room and pillar mining operations, as well as entry driving or roadway driving. Entry and roadway driving, along with room and pillar mining are operations that cannot use Lipinsky""s data recording scheme, and thus cannot use his control scheme because there is no parallel holes to record data in, to be applies anywhere else. These types of mining require that control be applied while the gamma detectors are being read, and does not require data recording and post processing, as does Lipinsky""s scheme.
Additionally, Lipinsky locates his detectors far back on the machine, and limits them to recording coal thickness data. This inhibits the adequacy of any control operation. This scheme also will not work where all coal is removed, and only rock is left at the roof and floor. The small detector scheme of the present invention, where we look for that dust cloud emitting a burst of gamma radiation, works well where all the coal or ore body is being extracted, and leaving only the seam boundary material.
The present invention addresses the shortcomings in Lipinsky""s patent at least in the following ways:
1. The present invention allows control of the miner in real time, and does not require application of previously recorded coal thickness data for control of the miner. Note that data was recorded over a period of hours during mining of the previous hole.
2. The current invention allows full seam extraction leaving only the seam boundary, and does NOT require coal to be left for it to operate, where Lipinsky requires coal to be left for his gamma detectors. These sense the boundary radiation to determine coal thickness, which is used as means of locating the boundary.
3. When the current invention uses a gamma sensor, it can be mounted on the machine anywhere that has a view of the cutter drum and material currently being cut, whereas Lipinsky""s invention is limited to being pointed towards roof or floor areas having a previously cut layer of coal.
4. The current invention uses a gamma sensor to determine the boundary by detecting a burst of gamma radiation when the boundary material is contacted by the cutter, and DOES NOT require coal thickness to be left like in the case of Lipinsky. Coal that is required to be left for the Lipinsky approach could be coal that is recoverable with the current approach.
5. The current invention control scheme can use any type of seam interface detector that will provide indication of cutter contact with the rock boundary and is not limited to gamma sensors.
The present invention provides a means to improve the control of cutting the roof and floor during underground extraction of coal or ore from the seam. Such roof/floor control is commonly referred to as xe2x80x9cHorizon Controlxe2x80x9d. With each forward advance of the mining machine in the seam, the control system locates the seam boundary(s) and directs the elevation of the machine""s cutter relative to the seam""s upper and/or lower rock boundary(s). Hence the extraction can be controlled to follow the seam boundary(s), avoiding the mining of rock and also providing control of the extraction height as may be required by the mining operation. Therefore, the control system which includes a microprocessor is capable of controlling either the upper or lower cutting horizons or both, during the mineral extraction process.
Sensors provide information for the system to calculate and determine upper and lower seam boundary locations (vertical elevations), machine attitude and cut profiles for the roof and floor as the machine moves continuously forward in a succession of sumping cycles during the coal or ore cutting operation. This information will be used by machine operators and/or the machine""s electro-mechanical control system to position the cutter in the seam or ore vein. The assemblage of components to be installed on the continuous mining machine will be referred to as the Horizon Control System. This system will make possible the cutting of a smoother, more uniform roof and floor, at the desired horizons (vertical elevations).
For reference, a xe2x80x9csumpingxe2x80x9d cycle for a continuous miner typically consists of the following steps:
1. Raise drum type cutter to the mine roof at the desired height (cutter is mounted on a boom that has a pivot at the opposite end).
2. The machine moves forward with the cutter entering the coal/ore face the selected roof height. The cutter travels or xe2x80x9csumpsxe2x80x9d in to the coal/ore a distance of xc2xd to ⅔ of its diameter.
3. The arm and the cutter are then lowered, cutting coal or ore from the face, until the cutter reaches the desired floor level. This is called the xe2x80x9cdowncutxe2x80x9d.
4. The machine then backs up to grade the floor and clean up (load) loose coal or ore into the shovel""s gathering head.
5. Cycle then repeats itself as the machine moves forward through the seam.
The Horizon Control System is installed on the continuous mining machine. It displays xe2x80x9creal-timexe2x80x9d guidance information to assist continuous miner operators in positioning the cutter head for desired roof and floor cuts or may be setup to automatically control positioning of cutter head through the miner""s electro-hydraulic controls. Using information from multiple sensors, the system provides an xe2x80x9cintelligentxe2x80x9d display of cutter height, measured from either the last cut floor or the next floor cut during a new sump cut. The display unit also indicates when the cutter has reached the required position for either the next roof or floor cut. However, the machine operator cannot always watch the display unit because he is also involved with other tasks occurring simultaneously, such as loading coal/ore transport vehicle. Therefore, when the cutter has reached the required position, a separate bright xe2x80x9ctarget lightxe2x80x9d is illuminated to notify operator to stop the cutter vertical travel. Alternately, as previously mentioned, the system""s microprocessor may direct the machine""s controls to stop cutter travel, in addition to turning on the xe2x80x9ctarget lightxe2x80x9d.
An Operator Interface Display Unit provides the means to display system information such as cutter height sensor values, calibration parameters, error conditions or other system operational information. The displays are controlled by the microprocessor. Displayed values may be in either English or Metric units. Prior to the new sump cycle, cutter height is displayed from the last floor cut. After the roof is cut and the sump down cycle is in progress (shearing coal/ore from the face); cutter height will be displayed to the operator as a distance relative to the new floor target. When the cutter arrives at the new target floor or floor cut position, the xe2x80x9ctarget lightxe2x80x9d will be turned on and the cutter travel will be stopped by the operator or by the system microprocessor.
Other features of the system are provided to facilitate setup, calibration and checkout. These include:
1) Switch or Key Pad Unit for entry of variable parameters into the system, such as machine geometry dimensions, mining requirements, calibration factors, limit settings, etc.
2) A Crawler Plane LED on the Operator Interface Display to be used as an aid in system calibration and checkout. When lit, the LED on the Operator Interface Display is used as an aid in system calibration and checkout. When lit, the LED indicates when the bottom of cutter is at the crawler plane reference. The crawler plane is a theoretical plane formed by bottom of the crawler treads on the left and right crawlers of the mining machine and projected forward to the cutter. It is noted that the vertical distance of cutter from projected crawler plane is an important geometric reference for the control system and is used in the calculation of cutter height (elevation).
3) An attitude sensor, such as an inclinometer, to measure machine roll (left to right inclination) that electronically controls an illuminated indicator on the display unit, providing a qualitative level at predetermined degree increments. External means can be used to re-level the machine based on the roll level display indicator.
A number of mining strategies may be used to extract the mineral from the underground seam, depending upon conditions. Choice of boundary sensors and control logic for cutting will vary with each of these strategies and seam geology. The most common extraction strategies, or Cases, are:
1. Full Seam Extraction of the mineral between upper and lower seam boundaries.
2. Partial Extraction and the leaving of residual mineral at one or both seam boundaries.
3. Minimum Height Extraction, taking all of the mineral and part of one or both boundaries.
4. Constant, Variable or Minimum Extraction Height as applied to above Cases 1, 2 and 3.
The horizon control system may utilize sensors of different types to detect the upper and lower seam rock boundaries, including such types as gamma, electromagnetic radiation, vibration, sonic, pick force, cutter motor current and optical reflectivity or imaging. The purpose of detecting and locating the seam boundaries is to be able to accurately control extraction of all or a desired portion of the coal seam and in certain situations to accurately control the amount of boundary rock taken. The latter would be true in low seams requiring rock removal to obtain additional height for equipment clearance.
In mining situations where all of the coal or ore is extracted from the given seam, i.e., none is left at the seam boundary, sensors must be able to detect when the cutter approaches or contacts the boundary. The cutter will rapidly (e.g. 3 to 5 inches per second) approach the boundaries in a vertical direction (normal to the plane of the boundary). In order to stop the cutter before or at the boundary, it is required that a stop command be issued to the hydraulic controls while the cutter is still several inches away from the boundary. In this mining environment, presently known sensors are not capable of detecting the boundary when the rapidly approaching cutter is still several inches away. However, it is possible for these sensors to detect when the cutter contacts the boundary. With that information, it is now possible to accurately determine the location (elevation) of the seam boundaries and to compute the desired horizon (elevation), relative to those boundaries, for the next roof and/or floor cuts made as the machine advances. Control methodology will be discussed later.
A small compact Gammna Sensor is one of the primary sensors that will be employed by the system to detect the cutter with a rock boundary. It can be used where boundary rock emits gamma radiation that is significantly different than that of the coal or ore in the seam. For example, usually the gamma radiation from common boundary rock materials such as shale or fire clay will be significantly higher that from the coal.
The system will utilize one or more gamma sensors to detect the rock boundary material. The gamma sensors may be placed in any location that will afford a view of the cutter and the material being cut. As the cutter approaches the roof or floor rock boundary (emitting gamma) the previously mined and exposed boundary may come into the sensor""s view increasing the amount of radiation detected. Also, additional radiation may be present to the gamma sensor, coming from the yet unexposed boundary directly above or below the cutting drum. As the cutter approaches the boundary, the coal between the boundary and the cutter becomes thinner allowing increased radiation from the boundary to reach the sensor. Some of this radiation will pass through the space between the spiral flutes of the cutting drum. Therefore, the total amount of radiation may further increase as the cutter nears the floor, providing an xe2x80x9cearly warningxe2x80x9d of the cutter approach to the floor. If the warning is sufficiently early, it may allow stopping of the cutter before it contacts the floor.
Alternately, another approach has been devised, that has proven in operation to be very reliable. In this approach, when the cutter contacts the floor a dust cloud made up of rock particles is generated by the cutting bits (teeth). Relatively high-energy gamma radiation is released by the dust cloud causing the sensor electrical output (gamma counts) to rise sharply (spike) in comparison with the previous sensor readings. This indicates to the system processor the time of boundary contact and the location (elevation) of the boundary. The system""s microprocessor will use this information for the control of subsequent cutting, as will be described later.
The control process for machine operation is described as follows:
1. Machine cutter""s vertical travel is stopped at a programmed (pre-determined) target height relative to the last known height (vertical elevation) of the seam boundary.
2. During cutter""s vertical travel (before being stopped) and as it approaches the seam boundary, sensors of various types will detect the proximity of or contact with the seam boundary.
3. If detected, the boundary""s vertical location can then be defined as a distance relative to machine cutter""s vertical location or height.
4. If boundary is not detected, then the last known boundary location (e.g. last cut) will be used.
5. Information as to the present and/or past location of the seam boundary is then used to calculate (estimate) the vertical target height for stopping the cutter on the next forward cutting cycle, that being a point approximately 2 feet forward of the machine""s current location.
6. The process is then repeated for each cutting cycle as the machine advances into the seam.
From the sensor information obtained in steps (3) and (4) above, it can be determined if the cutter has stopped at a point too low, too high or that is correct in relation to the seam boundary. In the event that the cut was too low, the target height (elevation) for the next cut cycle will be raised, or if the cut was too high, the target for the next cut will be lowered.
The horizon control system may use cutter elevation information to achieve limited horizon control where it is not possible to employ seam boundary sensors, such as gamma radiation or other types of detectors. This could happen if geological conditions for the mine would render boundary sensors ineffective. In this case the machine operator must be able to determine the location of at least one of the seam boundaries, i.e., either the upper or lower boundary rock. Using the cut elevation as adjusted and executed by the machine operator, the system then determines the location of the required next roof and floor cuts, using criteria determined as appropriate for the existing mining situation. As previously mentioned, when the cutter arrives at the required roof or floor cut position, the system may inform the operator by illuminating a xe2x80x9ctarget lightxe2x80x9d and/or automatically stop vertical travel of the cutter. At this point, if the operator further adjusts the cut elevation, this information will be used by the system in the determination of the required roof and floor heights for the next cycle.
It is noted that the process described herein will provide significant economic, environmental and worker health and safety benefits. The ability to guide the mining machine to extract only the desired part of the mineral seam will reduce rock dilution and other contaminants, e.g., sulfur, producing a cleaner more environmentally acceptable product. This will be particularly important to the coal industry and U.S. National energy goals.
It is an object of the present invention to provide a method and apparatus for increasing the efficiency of a continuous type mining machine.
It is a further object of the present invention to increase such efficiency by detecting the location of the seam boundaries and to guide the machine to achieve the desired cutting horizon (vertical elevations) relative to these seam boundaries.
In accordance with a preferred embodiment of the present invention there is provided a method and operation where the machine tracks and detects the location of the interface of the seam of coal and rock boundary of (The term xe2x80x9crockxe2x80x9d has been used to describe various types of boundaries in the coal seam). Data is received by the microprocessor that indicates that the detection has occurred and the microprocessor transmits this information to the control mechanism of the machine.